It is known in the art to produce toothed articles, such as bevel and hypoid gears, with cutting tools comprising a head portion in which a plurality of cutting blades are positioned, for example, stick-type cutting blades manufactured from bar stock such as shown in U.S. Pat. No. 4,575,285 to Blakesley.
In the type of cutting tool mentioned above, it is customary to provide a circular cutter body having a plurality of slots extending inwardly a predetermined distance from the periphery of the cutter body for receiving and positioning cutting blades in the cutter body. In many instances, extending about the periphery of the cutter body is a clamping ring (or locking ring) which is secured to the cutter body and in which is mounted means to clamp one or more cuffing blades in each of the positioning slots. Cutting tools including a clamping ring and blade clamping means can be seen, for example, in U.S. Pat. Nos. 4,621,954 to Kitchen et al.; 3,760,476 to Kotthaus; 4,093,391 to Bachmann et al.; or 4,197,038 to Hipp et al.
Traditionally, the positioning slots in a cutter head have been in a generally rectangular form of opposing side walls and an inner end wall which is perpendicular to the side walls. In machining these slots into the cutter head, it is understood that some clearance must be included in the slot dimensions in order for a cutting blade to be positioned in the slot. As such, even with the most accurate machining methods, there is always some amount of clearance between a cutting blade and a side wall surface when a cutting blade is clamped in position in a receiving slot.
With the square-cornered form of the prior art receiving slots and the clearance which exists between the cutting blade and a side wall surface of the slots, cutting blades have shown a tendency to twist in the receiving slots when subjected to the forces of some cutting operations thereby resulting in the formation of undesirable tooth geometries.
One arrangement for alleviating the problem of blade twist is addressed in international publication no. WO 97/39851 to Clark et al. The blade receiving slots comprise opposing side surfaces and an end portion comprising blade mounting surfaces which are angled toward one another with each mounting surface preferably extending at an angle of about 45 degrees with respect to its associated side surface. With this arrangement, a cutting blade with complementary shaped sides can positively seat against these angled mounting surfaces when clamped thus eliminating unwanted blade clearances as well as twisting of the blades during cutting.
The above-mentioned WO 97/39851 further discloses a cutter head comprising a plurality of double-dovetail shaped projections located on the outer portion of the cutter head body member. The double-dovetail projections are positioned in a complementary-shaped channel of a two-part cutter ring. The parts of the cutter ring are positioned above and below the projection and then drawn together by several screws thus securing the clamping ring to the cutter head body. By attaching the clamping ring in this manner, no heating of the cutter head is necessary and thus any heat-related distortions attributable to welding and/or heat shrinking are eliminated.
However, while avoiding heat-related distortions, formation of the double-dovetail projection requires significant machining accuracy which is quite time consuming. Tightening of the screws which join the two parts of the cutter ring may cause unwanted tension in the dovetail portion resulting in the formation of cracks between the projections of the cutter head during cutting operations or the dovetail portion may break off from the cutter head body member. Subsequent tightening blade clamping bolts adds more tension to the dovetail portion thereby further enhancing the possibilities of cracking and/or breakage.
It is an object of the present invention to provide a cutter head in which a cutter ring is attached to the cutter head body member in a manner which avoids the above-mentioned undesirable consequences.
It is a further object of the present invention to provide a cutter head in which the cutting blade mounting surfaces are arranged such that the strength of the cutter head is improved.
It is yet another object of the present invention to provide a blade clamping arrangement which allows the blade clamp to remain in the cutter head slot even in the absence of a cutting blade as well as in a position in the cutter head slot such that it does not impede insertion of a cuffing blade into the slot.